>> At this point (this may not have been wise, I realize) I decided to
>> copy over a back-up of the repository, made about a month ago.
>>
>> Now, when trying to interract with the database, I get this message:
>>
>> $ svn update
>> svn: REPORT request failed on '/svn/!svn/vcc/default'
>> svn: Reference to non-existent revision '231' in filesystem
>> '/Volumes/Data/svnrepo/db'
>>
>> What now?
>
> That last error is perfectly expected, since your working copy thinks
> it is at a later revision than actually exists in the repository.
>
> Regarding recovering your problem repository:

Ah. Well, you see, I have made this worse, then, I think. I completely
failed to back up the broken repository. (One of those great,
uncelebrated errors: Realizing just seconds after hitting "enter" that
one really shouldn't have.)

Um... am I sol, then? Can I do something to point my working copy at an
earlier revision? Is that possible? Something with switch maybe? Is
that insane?